Saturday, April 9, 2011

On events vs. data - the semantic view

I have written in the past about events vs. data, talking about the various roles that data stores can play in event processing.   recently I had a discussion in the more semantic level., about the differences between events and data.   The first distinction is that data (and also objects) do not have semantics in general, since anything can be stored in data, however event has a semantic meaning: something that happens!.    So the best comparison is to semantic data models, and in the picture above you can see the most simple (and common) semantic data model - the entity-relationship model.    As seen in this picture, entity is a term that designates some common name for individual beings that are classified to that term.   Person, department, equipment and experiment show in the picture are all entities.   None of them represent events,  since event is a different creature,  as mentioned it designates something that happens.   An event typically references entities.  For example, the event - Paul sold the bike to Peter is an event of type "sell" (if this is a general auction domain)  or "bike sell" (if this is a bicycle store domain).    In this case the event references three entities: 
  • Buyer:  entity of type person
  • Seller:  entity of type person
  • Item:   entity of type bike
Of course, in more general case the buyer and the seller can be corporates, and the item can be of any item type.    If we look at the description as a sentence,  the entity type is represented by a noun, while the event type is represented by a verb.    Note that not all verbs represent events though,  if we look at the picture above, the relationship  "requires" is a verb that designates that an experiment requires equipment, but it is not an event,  it is a static relationship among two entities,  so verb is not a sufficient condition for event, event represents a verb that indicate that something happened.     Models like the entity relationships model should be extended to include events.    


Lior Limonad said...

According to IS representation theory, Data actually also has semantics: every piece of data that we store must reflect something that we wish to represent. The difference between data vs. events lies actually in the semantic interpretation. That is: data is the very generic form of representation as mentioned above. However, the domain being represented includes various concepts and phenomena to which we can bind our semantic interpretation. For example: an 'interaction' is a phenomenon that we may wish to represent as Data. An 'Event' is another example. So I would argue that the comparison (i.e., events vs. data) is a somewhat unbalanced. One term reflects an IS construct (i.e., data), and the other (i.e., an event) is something that we may have an interest in capturing (an ontological concept).
With regard to ER diagrams, there are other possible interpretations that associate different semantic interpretations to the symbols (see

Opher Etzion said...

Hello Lior. Thank you for your comments -- as you mention DATA has multiple semantic interpretations. The paper you cite makes the interesting observation that people think differently about EVENTS and FACTS.